The present invention relates to an optical isolator which is positioned between a semiconductor laser as a light source and a light-transmitting part, for instance, in an optical transmission system to thus prevent a laser beam reflected by the optical transmission part from returning to the light source.
A copper wire conductor had been used in the information transmission and, recently, the information is transmitted by an optical fiber in the telecommunication by personal computer and the like on behalf of multimedia because the improvement in the capacity of the information transmission is desired and thus an optical fiber has larger transmission than a copper wire conductor. The base part of the telecommunication line has almost finished exchanging for the optical fiber. Though the branch part is under exchanging, the capacity of the information transmission in the branch part may be smaller than that of the base part because the optical fiber is more expensive than the copper wire conductor.
An optical isolator, which is the device of an optical fiber system to prevent a laser beam reflecting on an optical fiber face to a semiconductor light source, is required cheaper. However, optical elements incorporated into the optical isolator are often formed from expensive materials such as oxide single crystals. Moreover, the precision must strictly be controlled when combining such elements. As has been explained above, the production cost of the optical isolator increases because of high cost of assembly thereof and costs required for parts such as a holder.
As a means for saving the cost for assembly, there has been known a method which comprises adhering, in advance, optical elements to one another and then cutting it into pieces having a desired size. However, the optical isolator assembled according to this method is insufficient in the resistance to thermal shock and the adhered plane thereof easily undergoes peeling off due to temperature change. For this reason, if such an optical isolator is used over a long period of time, the quality thereof is impaired